Manufacture of electric radiant heating panels



Nov. 5, 1963 3,109,228

MANUFACTURE OF ELECTRIC RADIANT HEATING PANELS M T. DYKE 3RD., ETALFiled Aug. 10

INVENTORS. mazfl/v 7. awn? 3' E/WA w eAzLA ATTOE/VEYS resistor.

United States Patent Filed Aug. 10, 1959, Ser. No. 832,603 Claims. (61.29155.7)

'I'his invention relates to a process for manufacturing electric radiantheating panels and like elements.

An object of the invention is to provide a better and more economicalmethod of manufacturing such heating panels.

Another object is to simplify and improve the mass production of thesepanels.

These and other objects will in part be understood from and in partpointed out in the following description.

One of the first commercially available electric radiant heating unitsconsisted of a frame in which was mounted a sheet of tempered glass. Onthe rear side of the glass sheet theer was applied an electricalresistor in the form of a thin ribbon of metal which was heated bycurrent from a suitable source, such as a 115 volt power line. Most ofthe heat so generated in the resistor then would radiate from thefrontof the panel to provide very clean, comfortable heating.

Recently, to overcome the tendency of glass heating panels to shatterwith sudden changes in temperature'or from mechanical shock, panels ofporcelainized steel have been developed. The sheet steel center of sucha panel provides great mechanical strength while the porcelain coatingprovides an electric insulating surface on which a heating resistor canbe atfixed, and this coating also serves to promote radiation ofinfra-red heat energy from the panel.

One problem with such a panel is how to apply to the hard, smooth,impervious porcelain surface a resistor element which will cling tightlyto it in spite of repeated expansion and contraction during heating andcooling of the unit. It has been found that molten aluminum sprayed ontothe panel in a thin layer while the panel is at an elevated temperatureof from about 500 F. to about 700 F. will provide such a resistor. Now,a typical panel is designed to be connected directly to the power line(e.g. 115 v.). Thus, even though the aluminum is applied in a very thinlayer, to obtain a sufficiently high value of resistance it is necessarythat the aluminum be in the form of a narrow zig-zag strip folded backand forth along the panel so that its total length is much greater thanthat of the panel. Previously, attempts have been made to spray thealuminum directly over such a zig-za'g path, but working at the hightemperature required and in view of the limitations of the metalspraying equipment, as a practical matter is is impossible to do thiswith sufficient accuracy and uniformity. Accordingly, it has been thepractice to coat the porcelain surface of the panel with acontinuous,'uniforn1 layer of aluminum, and then to etch this aluminuminto the desired zig-Zag pattern.

This etching operation required as a first step the applying upon thecontinuous aluminumlayer of a special heat-and-chemically-resistantmaterial, such as silicone varnish, in the zig-zag pattern desired.Thereafter, the varnish-coated, aluminized panel was treated first in abath of hot alkali to remove the uncoated portions of the aluminum, andthen in a bath of acid to neutralize the alkali, this being followed bya thorough rinse in water to remove the acid. Also either before etchingor afterward electrical terminals had to be applied to the ends of theIf applied afterward, it was necessary then to remove the varnishcoating from the ends of the resistor;

it before, there was the problem of the solder and flux interfering withthe etching operation. It is evident, therefore, that this priorprocedure involves a number of steps, each of which had to be performedin a given order and some of which were critical as to time andtemperature. As a consequence, mass production of these units requiredan intricate and carefully regulated production line. Moreover, becauseof the relative slowness in production, a substantial inventory inpanels along the line was required. The present invention eliminatesthese difliculties, and yet the panels manufactured according to theinvention are actually better than previous ones.

In accordance with the invention, in one specific embodiment thereof, anelectric radiant heating panel is manufactured by first taking a sheetof porcelainized steel, cleaning it thoroughly and then applying to oneof its faces a thin coating of kaolin in the negative of the zigzigpattern desired for the resistor. This coating of kaolin isadvantageously applied to the panel as a wet paste through a silkscreen. Next, without the need for preliminary drying the panel israised to a temperature from about 500 F. to about 700 F. in the courseof which the kaolin is baked to a dry adherent coating. T hen while atthis temperature the panel is sprayed with a continuous, uniform thinlayer of aluminum and quickly thereafter while still hot it is plungedinto plain cold water. Though the metallic coating is continuous andcompletely covers the kaolin, because the metal was sprayed onto thepanel, it is microporous. Thus, Water readily penetrates it to the undercoating of kaolin which immediately absorbs the water, expanding andloosening in so doing. This blisters the metal layer loose from thepanel in those portions covered by the kaolin, the loosened metal andsoftened kaolin being then easily washed and brushed off. The aluminumin the remaining'areas where it directly contacted the porcelain SUI?face of the panel adheres tenaciously to'form a resistor in the zig-zagpattern desired. In fact, so tightly does this remaining metal adherethat in cleaning away the blistered metal and kaolin it is possible toscrub forcibly with a wire brush without damaging the electricalcontinuity of the resistor strip.

After this water bath and scrub, the panel is dried and electricalterminals applied. This is advantageously done by spraying thin areas ofcopper at the very end of the aluminum resistor and then soldering theterminals to this copper. There is no problem here of having first toremove from the resistor a varnish coating, or with the solder and fluxpoisoning a subsequent etching operation. Since no etching andneutralizing chemicals are used in this process, there are absolutely notrace amounts of acid or alkali remaining on the panel. Thus, theinsidious problem of failure of the resistor on a panel many years laterbecause of the slow but deadly corrosive action of these chemicals iscompletely eliminated. The thermal shock of putting the hot, justmetallized panels into cold water tends to reveal any defects in theirporcelain and metal resistor coatings. Moreover, immediately plungingthe hot panels into cold water promotes the blistering action of thekaolin and the removal of the unwanted portions of the aluminum. Thetime required to make a panel by this new process is less than half thatof the previous one. In addition, the hazards of volatile organicsolvents and alkali and acid fumes are entirely avoided.

'A better understanding of the invention together with a fullerappreciation of its many advantages will best be gained from thefollowing description given in connec tion with the accompanyingdrawings wherein:

FIGURE 1 shows a porcelain covered steel panel, on one :face of whichhas been applied a thin coating of kaolin in the negative of the patterndesired for the metallic resistor to be applied to the panel; a

scrubbing with a brush is desirable.

FIGURE 2 shows the panel with its kaolin coating in the process of beingsprayed with aluminum; and

FIGURE 3 shows a completed panel, the metal in the portions covered bythe kaolin having been blistered off in a water bath leaving a zig-zagresistor strip firmly anchored to the porcelain surface of the panel.

The panel shown in FIGURE-1 comprises a thin sheet steel core 12 whichis covered on its front and rear faces by tightly adherent porcelainlayers 14 and 16. The porcelain layers should preferably be free of pinholes and should completely coat the steel sheet to provide effectiveelectrical insulation. The steel should be freeof contaminants so thatthe porcelain and the resistor to be applied remain tightly adherentduring repeated heating and cooling of the panel. Porcelainized steelsheets. of this quality are available commercially.

Applied to porcelain face 14 of the panel in a negative zig-zag patternis a thin coating 18 of kaolin. important characteristics of thismaterial are that it withstands the high temperaures encountered; thatit'readily mixes and sofens in a safe, cheap solvent (e.g.' water); thatit dries to a thin, cohesive, sufficiently adherent coating; and that itreadily re-absorbs thesolvent to return to a soft condition. formulatedas follows: 1.0 pound of type #964 kaolin manufactured by Whittaker,Clark & Daniels, Inc.,

As an example, this material is screen can easily be washed clean; as aconsequence this bronze screening operation gives consistently excellentresults. Thus, the coating applied to every panel is uniform andprecise.

I vAfter a'panel has been coated with a pattern of kaolin, it is thenput ona conveyor and run through an oven where its temperature is raisedto a value from about 500 F. to about 700 F. In the course of thisheating, any water remaining in the kaolin is evaporated leaving a dry,thin, adherent coating on the panel. While at this elevated temperaturethe panel isv then sprayed with molten. aluminum in an even uniformlayer as illustrated in FIGURE 2. The aluminum is advantageously appliedfrom a stationary spraying unit 20, which can be a model number 24metallizing .gun'manufactured by Metallizing Engineering Co. ofWestbury, L.I., N.Y.,. while the panel one or more guns may be usedside-by-side to give a layer of suflicient evenness. The actualmetallizing operation on apanel 16 by 24 inches using three of thesemetallizing guns takes about seconds. After spraying, the still hotpanel with its metal coating is plunged into cold water, thekaolinimmediately expanding and selectively blistering the aluminum away fromthe panel as explained above. This blistering action is so effectivethat most of the kaolin and blistered metal can be wiped off the panelwith a soft rag. However, to be sure that all of the loose metal andkaolin are removed a thorough The panel is then dried.

FIGURE '3 shows the panel after it has been washed and this loosematerial removed. The aluminum which directly contacted porcelain layer14 remains very tightly adherent to it in the form of a zig-zag resistor22. The edges of the resistor are'even and correspond closely to theside lines of the kaolin coating. Thus, since this coating was exact insize in the first place, by controlling the uniformity of the. aluminumcoating from panel to panel, it is easily posible to produce panels withclosely uniform operating currents and temperatures.

Since resistor 22 is aluminum, it is desirable to spray over the areas24 and 26 at its ends, a thin coating of copper which can, unlikealuminum, readily be tinned.

Thereafter, electrical terminals can be soldered onto the copper byconventional techniques. If desired, resistor 22 can be covered with asuitable layer of, insulation, such as silicone varnish. v

In actual practice, a completed panel is mounted in a suitable framewith resistor 22 on the inside and porcelain face 16 exposed and servingas the heat radiating surface of the unit. The relative thickness ofsteel sheet 12, porcelain layers 14 and :16, kaolin coating 18, and

metal coating 22 are not shown to scale in the drawings. In an actualpanel, 16 by 24 inches, steel sheet 12 had a thickness of 0.049 inch;porcelain layers 14 and .16, 0.0 12 inch; kaolin layer 18, 0.006 inch;and aluminum layer I 22, 0.002 inch. Such a panel typically has anelectrical input of 1000 Watts andoperates with a surface temperature ofabout 350F. The operatingtemperature of this porcelainized steel panel,however, is not critical" and it can without damage to the panelfluctuate widely up or down; In the case of a heating panel usingtempered glass as its base, sudden changes in temperature,

or an increase in operating temperature aftera period of years operatingat .a lower temperature can cause it to shatter. I r

The above description of the invention is intended in illustration andnot in limitation. Various changes may occur to those skilled in the artand these may be made without departing from the spirit or scope of theinven tion as set forth. y

We claim:

1. An improved method of applying a tightly" adherent resistor elementhaving a desired pattern and resistance toa supporting surfacecomprising the steps of coating a and said panel is .subjectedto thermalshock to reveal" possible defects.

3. A process for manufacturing high quality electric radiant heatingpanels and the like at lower cost, said process comprising the steps ofapplying to a base panel 'by' silk screen printing a paste-like mixtureconsisting principally of kaolin and water in a zig-zag pattern and in athin layer, heating said coated panel to a substantially ele;

vat'ed temperature, spraying said heated panel with aluminurn-like metalin a thin continuous layer, thereafter putting Water on said metallizedpanel to remove the kaolin and the metal immediately covering it, andthen applying electrical terminals to end portions of the remainingmetal on said panel, whereby said panel is free of traces of corrosivechemicals and said remaining metal remains tightly adherent duringrepeated heating and cooling.

4. An improved method of making aresistance unit suitable for radiantheating and the like, said method com prising the steps of taking a basemember having an insulating surface and coating it With a cohesiveadherent patterned layer at least several mils thick of a paste-likemixture consisting primarily of kaolin and water, heating said memberand layer to an elevated temperature, spraying with a generally uniformlayer of aluminum-like metal to a thickness of several mils, and finallywashing said metallized member in water to cause said mixture to blisteroff undersired portions of the sprayed metal.

5. An improved method of making an electrical radiantv heating panelcomprising taking a clean base sheet having References Cited in the fileof this patent a smooth insulating surface, coating it with a patternedUNITED STATES PATENTS layer of Wet clay material which is driable into athin J cohesive adherent layer, heating said coated sheet to a f g isubstantially elevated temperature above the drying point 5 of said claymaterial, applying to said heated sheet a FOREIGN PATENTS thincontinuous uniform porous layer of conductive metal,

and Washing said metallized sheet in Water to remove ungfgif gi x 5 ad 1. 1 1 wanted metal an sad clay material to cave on said 150,890swltzefland Feb. 16) 1932 base sheet a tightly adherent resistor havinga desired 10 shape and resistance.

3. A PROCESS FOR MANUFACTURING HIGH QUALITY ELECTRIC RADIANT HEATINGPANELS AND THE LIKE AT LOWER COST, SAID PROCESS COMPRISING THE STEPS OFAPPLYING TO A BASE PANEL BY SILK SCREEN PRINTING A PASTE-LIKE MIXTURECONSISTING PRINCIPALLY OF KAOLIN AND WATER IN A ZIG-ZAG PATTERN AND IN ATHIN LAYER, HEATING SAID COATED PANEL TO A SUBSTANTIALLY ELEVATEDTEMPERATURE, SPRAYING SAID HEATED PANEL WITH ALUMINUM-LIKE METAL IN ATHIN CONTINUOUS LAYER, THEREAFTER PUTTING WATER ON SAID METALLIZED PANELTO REMOVE THE KAOLIN AND THE METAL IMMEDIATELY COVERING IT, AND THENAPPLYING ELECTRICAL TERMINALS TO END PORTIONS OF THE REMIANING METAL ONSAID PANEL, WHEREBY SAID PANEL IS FREE OF TRACES OF CORROSIVE CHEMICALSAND SAID REMAINING METAL REMAINS TIGHTLY ADHERENT DURING REPEATEDHEATING AND COOLING.